Foundation for a sunroom addition....

I'm months (if not years ) from building on an addition on the side of our house. I plan on going out 12 feet, running the length of the house, around 30'. I want to make this room into a sunroom, breakfast room.

No plans yet, just lots of thinking. I know around here I'll have to foot the foundation (I think 24"). If I were to make the floor level with the existing floor of the house, it would be around 2' off the ground (I'll probably have a could of steps down). The rest of the house has a full basement, I'm not interested in digging a basement addition to the structure. I'd like to add HVAC as well, so I can use it year around.

I'm in the early stages of the thinking process, what would people recommend for a foundation? I know I'll be looking at more details regarding code, etc. but in the meantime, any pratical general suggestions would be appreciated. I'm not ready for a lot of details at this point but just some general guidelines. I'll end up with the floor at least 1' off the level of the ground, any ideas that keep heat/cold factors in mind are appreciated!

At least around here, you would have 2 choices -- either the floor is going to be a slab, OR it's going to be 18" min. above grade. No such thing as a floor that is only 12" above grade.

Also, as soon as you say that you want the room to be "conditioned" (HVAC), you have just gotten into a whole new set of criteria for the room. It will have to be built as an addition to the house, not as a "patio room". THAT changes everything! Changes the energy standards you have to meet, changes the types of construction that you can use, changes the way it is taxed, ... EVERYTHING!

Everything changes, ain't that the truth about almost every project I start!

Actually, my latest musings is to pour a concrete crawl space first. Do you have any idea of the cost ratio between a crawl space & a full basement? In other words, if I excavate & pour for a crawl space, how much more would doing the whole thing be? 2, 3 times as expensive? I guess is what I can look at is if it isn't going to cost that much more, maybe I should save my pennies & go the full route. I would imagine that the cost of that basement per sq. ft. would be significantly lower than an above grade addition, there may be some added value there.

Anyhow, thanks for the reply - if I continue w/ this full blown project (proabably a year away, but who knows), what forum would you suggest I use for further advise? Home Plans? Perhaps I should start out in each section, codes, then basements, ...